A vehicle air bag assembly functions to protect a vehicle occupant during a crash or collision. The principal components of a vehicle air bag assembly are a receptacle, an air bag located within the receptacle, and an inflator positioned to supply inflation fluid to the air bag. When the inflator supplies the inflation fluid, the air bag is forced out of the receptacle and inflated. In this manner, the air bag will cushion a vehicle occupant against impact with a structural part of the vehicle. On the driver side of a vehicle, an air bag assembly is commonly incorporated into the vehicle steering wheel. On the passenger side of a vehicle, an air bag assembly is commonly incorporated into the vehicle instrument panel.
A typical inflator includes first and second housing members which are coupled together to form a closed chamber for a source of inflation fluid. The fluid source may comprise a gas generating composition which, when ignited, rapidly generates an inert non-toxic gas, such as nitrogen, to inflate the air bag. During this generation process, the inflator will be subjected to intense thermal and mechanical stresses. For example, in a driver side air bag assembly, pressures in the range of 3000 psi are commonly produced during the generation process. In a passenger side air bag assembly, significantly higher pressures approaching 10,000 psi are typically encountered. Consequently, the inflator housing members, and the coupling between these housing members, must be able to withstand these stresses.
In the past, inflator housing members have been coupled together by threaded coupling arrangements (see e.g. U.S. Pat. No. 4,938,501 to Wipasuramonton) and welded coupling arrangements (see e.g. U.S. Pat. No. 4,890,860 to Shneiter). These coupling arrangements, while sufficient to withstand the stresses of the gas generation process, have not been compatible with certain manufacturing concerns. For example, threaded coupling arrangements require that the machining of the threads at a very tight tolerance (0.003 inch) and a close inspection of the threads to ensure that such tolerances are met. Consequently, the machining of the threads is an expensive process. With respect to welded coupling arrangements, such arrangements usually necessitate the use of thick housing members and/or costly, time-consuming weld inspections.
Another manner of coupling together inflator housing members is set forth in U.S. Pat. No. 4,907,819 to Ceuvas. This patent, which is directed towards an inflator for a driver side air bag assembly, disclose a "non-welded" coupling arrangement between inflator housing members. Specifically, the Ceuvas inflator housing members are coupled together by rolling a coupling portion, or skirt, of a first housing member radially inward over a peripheral edge of a second housing member.
The Ceuvas patent notes that this "non-welded" coupling arrangement eliminates the manufacturing disadvantages commonly associated with threaded and/or welded coupling arrangements. However, applicant believes that the Ceuvas coupling technique can not be used with an inflator for a passenger side air bag assembly. The housing members, which the Ceuvas patent states are preferably aluminum, must be of a suitable thickness to withstand the stresses of the generation process. While applicant believes that an aluminum housing member having a thickness in the range of 0.050 inch could withstand driver-side stresses, applicant also believes that an aluminum housing member would have to possess a thickness in the range of 0.25 inch to withstand significantly higher passenger-side stresses. Applicant believes that a housing member having a thickness in this range could not be easily and/or effectively rolled inwardly to form the Ceuvas coupling arrangement.
Additionally, it is often desirable for inflator housing members to be coupled together in a manner which is tamperproof. "Tamperproof" in this context means that the inflator housing members cannot be uncoupled with standard tools, such as a screw driver or a conventional wrench. This feature is sometimes particularly important in passenger-side air bag assemblies because portions of the inflator will be accessible during mechanical repair of the vehicle.
For these reasons, applicant believes a need exists for an inflator coupling arrangement which: (i) may be used with both driver-side and passenger-side air bag assemblies; (ii) is compatible with manufacturing design concerns; and (iii) is tamperproof.